1. Field of the Invention
The present invention relates to polyolefinic compositions having elastic properties and to the use thereof for the manufacture of shaped articles for biomedical use.
2. Description of the Prior Art
The most used material for the manufacture of flexible articles for biomedical use is represented by the plastified poly-vinyl chloride (PVC). The high characteristics of flexibility of the plastified PVC are due to the plasticizers contained in it.
However, the migration and extractability of plasticizers in biological liquids, with the consequent possible negative effects on the health of the patient represent a still unsolved drawback.
In addition, it has to be taken in mind the surface migration of the additives based on organo-polysiloxane oils used in PVC as external lubricants to give to the PVC surface a critical surface tension intended to avoid blood coagulation phenomena. In fact, the organo-polysiloxane compounds tend to exude from the PVC surface thus causing problems deriving from their poor compatibility with blood (see European patent application EP-A-287 482).
Therefore, the need of materials substitutive of PVC in these fields is highly felt.
Other materials suitable for the manufacture of flexible devices for biomedical use are the styrene-ethylene-butene-styrene block copolymers (SEBS). SEBS modified with polysiloxanes have been for example suggested as substitutive of PVC and silicon resins for the realization of some devices, such as endotracheal tubes (U.S. Pat. No. 4,386,179). These copolymers combine good properties of optical transparency and flexibility also at low temperatures.
U.S. Pat. No. 4,335,225 describes the preparation of high molecular weight polypropylene showing elastomeric characteristics and processable by the technologies of thermoplastic materials and suggests a possible use of this polypropylene for the manufacture of some articles for biomedical use. The polymerization is carried out using as catalyst the product of the reaction of an organic derivative of zirconium, generally tetra-neophil-zirconium, with hydroxilated alumina. However, the content of aluminium in the polymer obtained is always very high, higher than 1000 ppm. Till now, the above mentioned materials did not find any meaningful application in the biomedical field.
It has now unexpectedly been found a new polymeric material suitable for the manufacture of articles for biomedical applications, which combines a good set of mechanical properties with good optical properties and that, furthermore, does not show problems related to the extractability of metals in biological fluids.
Therefore, an object of the present invention is a thermoplastic composition comprising:
(A) from 1 to 99% by weight of a propylene amorphous polymer having the following characteristics:
[xcex7] greater than 1 dl/g
% syndiotactic diads (r)xe2x88x92% isotactic diads (m) greater than 0;
less than 2% of the CH2 groups contained in sequences (CH2)n, with n greater than 2;
Bernouillianity index (B)=1xc2x10.2;
(B) from 1 to 99% by weight of a component selected from:
(B1) a copolymer of propylene with at least a comonomer selected from ethylene and the xcex1-olefins of formula CH2xe2x95x90CHR wherein R is an alkyl radical containing from 2 to 8 carbon atoms, said copolymer containing at least 85%, preferably 90-99%, by weight of units deriving from propylene, and
(BII) a polyolefinic composition comprising:
(a) 10-50%, preferably 10-40% and more preferably 20-35%, by weight of at least a polymer selected from a propylene homopolymer having an isotactic index higher than 80, preferably higher than 85, and a copolymer of propylene with at least a comonomer selected from ethylene and the xcex1-olefins of formula CH2xe2x95x90CHR wherein R is an alkyl radical containing from 2 to 8 carbon atoms, said copolymer containing at least 85%, preferably 90-99%, by weight of units deriving from propylene,
(b) 0-20%, preferably 0-15%, by weight of a copolymer containing ethylene, insoluble in xylene at room temperature, and
(c) 40-80%, preferably 50-70%, by weight of a copolymer containing 10-40% by weight of units deriving from ethylene, 90-60% by weight of units deriving from at least a comonomer selected from propylene and the xcex1-olefins of formula CH2xe2x95x90CHR wherein R is an alkyl radical containing from 2 to 8 carbon atoms, 0-5% of units deriving from a diene, said copolymer being soluble in xylene at room temperature and having an intrinsic viscosity comprised between 1.5 and 4 dl/g;
wherein the sum of components (b) and (c) is. comprised between 50 and 90% by weight on the polyolefin olefinic composition and the ratio of the amounts by weight of components (b)/(c) is lower than 0.4.
Another object of the present invention is a shaped article for biomedical use, obtainable from a thermoplastic composition according to the invention.
The ratio of the amounts by weight of components (A)/(B) in the composition of the present invention is preferably comprised between 10:90 and 90:10 and, more preferably, between 25:75 and 75:25.
The propylene polymers of the component (A) in the composition of the invention, together with the process for the preparation thereof, are described in the European patent application EP-A-604 917, the content of which is intended included in the present description.
These propylene polymers are amorphous, can be obtained directly from the polymerization reaction of propylene, and have the following characteristics:
(a) intrinsic viscosity [xcex7] greater than 1 dl/g;
(b) the percentage of syndiotactic diads (r) minus percentage of isotactic diads (m) is greater than 0;
(c) less than 2% of the CH2 groups are contained in sequences (CH2)n, with n greater than or equal to 2;
(d) Bernouillianity index (B)=1+0.2.
These propylene polymers are essentially free of crystallinity. Their melting enthalpy values are generally lower than 20 J/g and, preferably, lower than 10 J/g. In most cases, they have melting enthalpy values of 0 J/g.
Preferably, the above mentioned propylene amorphous polymers show intrinsic viscosity values higher than 1.5 dl/g and more preferably higher than 2 dl/g.
13C-N.M.R. analysis carried out on the above mentioned ethylene amorphous polymer gives information on the tacticity of the polymeric chains, that is, on the distribution of the configurations of the tertiary carbon atoms.
The structure of these polymers appears substantially atactic. Nevertheless, it is observed that syndiotactic diads (r) appear to be more numerous than the isotactic ones (m). Preferably, %rxe2x88x92%m greater than 5.
The Bernouillianity index (B), defined as:
B=4[mm] [rr]/[mr]2
has values near the unit, in particular comprised within the range 0.8-1.2 and preferably comprised within the range 0.9-1.1.
The structure of these propylene polymers appear to be highly regioregular. In fact, from the 13C-N.M.R. analysis signals relating to sequences (CH2)n, wherein n greater than 2, are not detectable. Therefore, less than 2% and preferably less than 1% of CH2 appears contained in sequences (CH2)n, wherein n greater than 2.
Molecular weights of the above mentioned propylene polymers are not only high, but distributed within rather narrow ranges. An index of the distribution of molecular weight is represented by the ratio Mw/Mn which appears to be generally lower than 5, preferably lower than 4 and more preferably lower than 3.
The polyolefinic compositions which form the component (BII) of the composition according to the present invention, together with the process for the preparation thereof, are described in European patent application EP-A-472 946, the content of which is intended included in the present description.
The thermoplastic compositions according to the invention can contain additives able to give particular properties to the articles for the manufacture of which the composition is designed.
Additives useable are those generally used in the polymeric thermoplastic compositions such as for example stabilizers, anti-oxidizing agents, anti-corrosion agents, etc.
Furthermore, the compositions of the invention can contain organic or inorganic, also polymeric, fillers. These additives and fillers can be used in conventional amounts, as known to those skilled in the art or as easily determined by routine tests, generally up to 5% by weight on the final composition.
The thermoplastic compositions of the present invention can be prepared by admixture of the components in internal mixers of the Banbury type.
The compositions of the invention are generally obtained in form of pellets. These can be transformed into manufactured articles by the generally used processes for the processing of thermoplastic materials, such as injection molding, extrusion, etc. The obtained manufactured articles are endowed with elasto-plastic properties particulary interesting for biomedical articles.
The high elasto-plastic properties of the compositions of the invention are made clear by low tensile set values; for example, the residual deformation after 100% elongation (10 min., 23xc2x0 C.) is generally lower than 30%. Furthermore the compositions of the invention are characterized by high ultimate tensile strength, generally higher than 4 MPa, with deformation generally higher than 300%.
The optical properties are evaluated by measuring on a 1 mm thickness plate, the amount of transmitted light which deviates from the original incidence angle (xe2x80x9chazexe2x80x9d). The composition of the invention are characterized by xe2x80x9chazexe2x80x9d values generally lower than 60%, preferably lower than 50%.
Therefore, the composition of the invention, differently from their single components, shows a good combination of elastomeric properties, thermoplastic processability and optical transparency.
In fact, the component (A), although showing very good optical properties, generally is not endowed with satisfactory values as to the ultimate tensile strength.
On the contrary, the component (B), endowed with high ultimate tensile strength, has insufficient light transparency properties, and the elastic recovery properties are worse in comparison with the compositions of the invention (higher tensile set values).
Taking into account the above mentioned mechanical properties and the good compatibility with blood and soft tissues, the compositions of the invention are particulary suitable for the manufacture of articles for biomedical applications.
As articles for biomedical applications, the articles for the contact with biologic or injectable fluid are intended. Examples of manufactured articles according to the present invention are tubes for enteral or extra buccal feeding, tubes for peristaltic pumps, catheters, devices for hemodialysis, bags for blood or plasma, seals for syringes, artificial organs and similar applications.
Owing to the transparency characteristics of the compositions used for the manufacture of the above mentioned articles, particulary interesting are the devices for containing, supplying, drainage and transport of blood and biologic or physiologic fluids, such as for instance intravenous catheters, dialysis tubes, bags for blood and physiologic solutions and similar applications. In fact it is easy to detect inside the devices the presence of bubbles, blood coagules, scales of biomineral origin inside the devices for dialysis, presence of extraneous material, etc.
The possibility of sterilization by treatment with radiations, in particular gamma radiations, according to known technologies or by chemical way (aseptic sterilization), the resistance to solvent used in hospitals, the non adsorption of drugs, the weldability according to known welding techniques, the dimensional stability are further interesting characteristics of the manufacture articles of the invention.
Further advantages are made clear by the examples which are given to illustrate and not to limit the invention.
The intrinsic viscosity [xcex7] was measured in tetrahydro-naphthalene at 135xc2x0 C.
The 13C-N.M.R. analysis of polymers were carried out with an instrument Bruker AC200 at 50323 Mhz, using C2D2Cl4 as solvent (about 300 mg of polymer dissolved in 2.5 ml of solvent) at a temperature of 120xc2x0 C.
The molecular weight distribution was determined by GPC carried out on instrument WATERS 150 in orthodichlorobenzene at 135xc2x0 C.
The Differential Scanning Calorimetry measurements (DSC) were carried out on an instrument DSC-7 by Perkin Elmer Co. Ltd. according to the following procedure. About 10 mg of sample were heated from 40xc2x0 C. to 200xc2x0 C. at a rate of 20xc2x0 C./min; the sample was kept at 200xc2x0 C. for 5 minutes and thereafter it was cooled to 40xc2x0 C. at the same rate. Thereafter a second heating scan was carried out according to the previous conditions. The values reported are reheat values.
The ethylene content in copolymers was determined by infrared spectroscopy (I.R.).
Melt Flow Ratio (MFR) values were determined by the method ASTM-D 1238, conditions L.
Physico-mechanical characterizations were carried out according to the hereinafter indicated methods:
The above mentioned physico-chemical characterizations were carried out on specimens cut from a 1 mm thickness plate, prepared by compression molding under the following conditions: 5 minutes at 200xc2x0 C. in the absence of pressure, then 5 minutes under pressure, thereafter cooling to 23xc2x0 C. under pressure with circulating water.